If your new to Cats, I'd prob get started with something like a pictus, or a 4line pim, Jaguar, Raphs anything like those guys are all pretty bullet proof and are great beginner cats.
As for moderate to harder species, it really depends on what your fish keeping history has been up till now. There are really only 2 types of catfish for Fish keeping... Easy and extremly hard...the Hard ones would be something like a Tig... very sensative to water, food, tank conditions ect... If space is no issue and your looking for the wow factor... REDTAILED Catfish all the way... Tigershovelnose is also a Must have in these tanks...Once you have those two... it's pretty much impossible to not want a hybrid of the two LOL, Lima shovelnose is the smaller tank species which can be great to have around, they get to around 18" on average so the tank needs to be able to be at least that wide.
Ok enough rambling... time to get back to the renovations LOL